98 GSX Ltd "on one cylinder" < 4000 RPM

[strean]

Hi! all

My 98 GSX Limited feels like it's running on only one cylinder from idle up to around 3700 RPM, at which point the "mis-fire" becomes less regular; at 4K and up runs smooth and fast.

Initially, I've cleaned the carbs and fuel filters, replaced the needle valves (came from the prev owner with 2.3's which I replaced with the same), replaced the fuel lines and fuel selector. Compression was a bit low on one cylinder at the time (iirc about 127 & 115) so I did the top end and replaced the reeds. Still have the "mis-fire" ...

Just did pop-off pressure test (though not sure if this would contribute to my problem?) and I'm at 22 & 21 psi. One thing I noticed is that though both valves hold pressure, after they pop, one side loses almost 100% (maybe 5 psi left) of its pressure whereas the other loses only about 5-10 psi. (115 gram springs on both sides, arms don't look noticeably bent) If one needle valve wasn't re-sealing quickly could that cause one of the cylinders to run rich, causing the "mis-fire"?

Thanks for any help!


--
Mike

 

[wfo speedracer]

Check the small reed valve on the jet cover plate very closely , it will cause the problem you describe.

 

[Mekanix]

Check the small reed valve on the jet cover plate very closely , it will cause the problem you describe.

+1, if that is leaking or very weak, your basically flooding that cylinder and it will feel like a misfire until around 4000 where you would normally be running on the main jet.

I would think that you may even be able to see the fuel dribbling out of the main jet ventury or what could be happening is that air is being drawn in past that and into the pilot circuit...

 

[strean]

Hey thx for the replies. I checked out the check valves and they look OK to me [attached pix, just noticed because of wd40 underneath, in the pic one looks misshapen though in real life it is fine] In fact I'm not positive but I may have replaced these - I don't recall if they came with the carb rebuild kit I got from OSD, thinking yes. Also gently pushed them open and they feel about the same.

 

[wfo speedracer]

Okay since you have the carbs off the next step is to get a can of carb cleaner and some safety glasses, poke the straw on the carb cleaner into the pilot jet, put on the safety glasses ! Now flip the carbs upside down and slightly open the butterfly till you see the bypass holes, spray carb cleaner through the pilot jet and verify that it is in fact coming out of each of the bypass holes, if it isn't find a very small piece of copper wire, fashion it into an L and use the wire to poke each of the bypass holes, then try the carb cleaner again and verify it is coming out of all the holes.

 

[strean]

Done - the bypass holes seem clear. Have an even spray of carb cleaner out of the 3 small and 1 larger hole. Also just noticed the cross drilled passage in the check valve plate, and made sure that was clear (it was)

 

[wfo speedracer]

May be an issue with the coil then, does your ski have one coil or two ?

 

[strean]

One coil

Resistance on the primary and secondary are within range - though I know it's not a definitive test.